1. Field of the Invention
The present invention generally relates to recording methods and apparatuses using an intermediate transfer medium and, more particularly, to a method and apparatus for forming images on the front side and back side of a sheet-like recording medium such as printing paper by forming images on an intermediate transfer medium by applying a liquid onto a layer of the intermediate transfer medium formed on an intermediate transfer member and transferring the thus-formed images to the front side and back side of the sheet-like recording medium.
2. Description of the Related Art
A recording method such as an inkjet recording method, in which droplets of a liquid containing a colorant are projected onto a recording medium in accordance with image signals, can be accomplished by an apparatus having a relatively simple, compact and light. structure and a low noise. However, the inkjet recording method has a problem with respect to print quality in that the results of printing differ due to differences in the quality of printing papers such as synthetic paper, regular paper or inkjet paper. Particularly, when the printing is performed on regular paper with general use water soluble ink, there is a problem in that the resolution of a printed image is decreased due to running of ink on the printing paper or penetration of ink to the back side of the printing paper. Additionally, there is a problem in that the printed ink image may be smeared due to undried ink being touched when the printing paper having the ink image thereon is ejected from the inkjet apparatus. Further, since water soluble ink is normally used in the normal inkjet recording method, when the printing is performed on regular printing paper, printing cannot be performed on the back side of the printing paper after printing the front side of the printing paper due to running of ink on the printing paper or penetration of ink to the back side of the printing paper.
In order to eliminate the above-mentioned problems, intermediate transfer methods have been developed such as disclosed in U.S. Pat. Nos. 4,538,156 and 5,099,256. In the intermediate transfer methods, an ink image is formed on an intermediate transfer member according to the inkjet recording method, and, thereafter, the ink image is transferred onto a recording medium such as printing paper. According to the intermediate transfer method, the recording head can be located remote from the printing paper, which prevents clogging of the nozzles of the recording head due to adhesion of paper dust. However, the intermediate transfer method has problems in that, when droplets of ink are provided on the intermediate transfer member, the droplets may improperly spread or move on the intermediate transfer member. Additionally, if color ink is used, mixing of colors may occur which causes an image quality to deteriorate. Further, there are issues to be solved such as the transferring efficiency to a recording medium such as paper or the quality of the transferred image on the recording medium. For example, running of ink or penetration of ink to the back side of the printing paper is one of the issues to be solved.
In order to solve the above-mentioned problems, Japanese Laid-Open Patent Application No. 62-92849 discloses an improved intermediate transfer method in which the droplets of ink on the intermediate transfer member are dehydrated so as to transfer the condensed ink droplets to a recording medium such as paper. This method is advantageous in forming a clear image. However, the condensation of ink requires a considerable time interval and amount of heat energy, and also requires means for preventing scattering of water vapor from the ink droplets. Accordingly, this method cannot satisfy the demand for high-speed printing for both sides of a recording medium, the demand for energy saving and the demand for a further increase in the resolution of the image.
Japanese Laid-Open Patent Application No. 5-200999 discloses an intermediate transfer method in which droplets of ink are applied to a water absorbing layer on the intermediate transfer member so as to dehydrate the droplets, and the dehydrated droplets are transferred to printing paper. The water absorbing layer is made of a film or fibrous material which swells by absorbing water at a low temperature and releases the absorbed water due to a phase change at a high temperature. That is, in this method, water or solution in the droplets of ink is removed by the water absorbing layer, and the condensed ink is transferred onto the printing paper. Accordingly, this method is advantageous in forming a clear image. However, similar to the method disclosed in Japanese Laid-Open Patent Application No. 62-92849, the condensation of ink requires a considerable time interval and a considerable amount of heat energy, and also requires means for preventing scattering of water vapor from the ink droplets. Additionally, this method requires means for removing the water or solution from the water absorbing layer. Accordingly, this method cannot satisfy the demand for high speed printing for both sides of a recording medium, the demand for energy saving, the demand for a further increase in the resolution of the image and the demand for reducing the size and weight of the apparatus.
Japanese Laid-Open Patent Application No. 7-89067 discloses an inkjet recording technique in which droplets of ink are provided on a surface active agent applied on the intermediate transfer member so as to form an ink image on the surface active agent so that the thus-formed ink image is transferred onto a recording medium. Generally, the surface active agent has a function to reduce surface tension of a liquid or a solution. Thus, when a droplet of ink whose major component is water is provided onto the surface active agent by an inkjet recording method, the surface tension of the droplet of ink is reduced. The reduction in the surface tension results in the spreading of the droplet of ink. Accordingly, the diameter of the droplet of ink on the surface active agent is larger than the diameter of the droplet of ink projected by the inkjet nozzle. Thereby, it is difficult to achieve a high-resolution, sharp image by the technique using the surface active agent. Additionally, since the droplet is transferred onto the recording medium such as paper together with the surface active agent, the droplet of ink and the surface active agent are absorbed by the recording medium, which results in the running and penetration of ink. Thus, the technique using the surface active agent cannot be used for both-side printing.
Additionally, Japanese Laid-Open Patent Application No. 10-58664 discloses a method in which droplets of ink containing quarternary ammonium salt are provided onto an anionic ion exchanging resin layer on the intermediate transfer member so as to transfer the droplets of ink after the droplets are subjected to a chemical reaction during the conveyance of the droplets by the intermediate transfer member. This method is advantageous in improving the transfer efficiency. However, since the nature of the colorant contained in the ink is changed by the ion exchanging resin layer, the color of the ink may be slightly changed. Generally, the ion exchanging resin layer does not have a function to absorb water contained in a droplet of ink. Accordingly, the droplet of ink applied to the ion exchanging resin layer is subjected to a change in its nature, but concentration of ink in the droplet does not change. That is, the droplet of ink is transferred onto a recording medium without change in the concentration of ink. Thus, running of ink, color mixing or penetration of ink to back surface occurs in the transferred ink image. Additionally, when the ion exchanging resin layer is heated so as to restore the function of the ion exchanging resin layer, an ammonium gas is generated. Accordingly, the stench of the ammonium gas causes pollution of air. Further, there is a problem in that a maintenance operation must be frequently performed so as to restore the ion exchanging resin layer. Further, this method cannot satisfy the demand for high-speed printing for both sides of a recording medium, the demand for energy saving, the demand for a further increase in the resolution of the image and the demand for reducing the size and weight of the apparatus.
In order to solve the above-mentioned problems, Japanese Laid-Open Patent Application No. 11-188858 suggests an intermediate transfer method using a. polymeric powder being applied onto an intermediate transfer member, the polymeric powder having a liquid absorbing characteristic. In this method, a layer of the polymeric powder is formed on an intermediate transfer member before a liquid is provided onto the intermediate transfer member so as to form an image. The polymeric powder dissolves in the liquid or swells by absorbing the liquid, and increases the viscosity of the liquid. Additionally, the layer of the polymeric powder layer can be easily removed from the intermediate transfer member. However, this patent document does not refer to a method for recording images on both sides of a sheet-like recording medium such as printing paper without deterioration of the image quality due to running or penetration of ink.
It is a general object of the present invention to provide an improved and useful intermediate transfer recording method in which the above-mentioned problems are eliminated.
A more specific object of the present invention is to provide an intermediate transfer recording method which can record images on both sides of a sheet-like recording medium while preventing the image formed on one of the front and back sides from being influenced by the image formed on the other side.
In order to achieve the above-mentioned objects, there is provided according to one aspect of the present invention a method for recording images on a sheet-like recording medium having a first side and a second side opposite to the first side, the method comprising the steps of:
forming a layer of a material on an intermediate transfer member;
applying a liquid to the layer formed on the intermediate transfer member so as to form a first visible image on the layer, a viscosity of the liquid being increased by the material forming the layer on the intermediate transfer member;
transferring the first visible image onto the first side of the recording medium;
forming another layer of the material on the intermediate transfer member:
applying the liquid to the layer formed on the intermediate transfer member so as to form a second visible image on the layer; and
transferring the second visible image onto the second side of the recording medium.
According to the present invention, visible images are provided on both the first and second sides of the recording medium. The formation of the visible images are performed by using the material which increases the viscosity of the liquid such as ink for forming the visible image. Accordingly, when the liquid is transferred onto the recording medium such as printing paper, the liquid does not run on or penetrate into the recording medium due to the increased viscosity. Thus, the visible images can be formed on both the first side and the second side of the recording medium while the visible image on one side is not influenced by the visible image on the other side.
In the present invention, the material forming the layer on the intermediate transfer member may have a liquid absorbing property, and the material may be in the form of powder.
When the layer is formed by the powder, only the portion of the layer wetted by the liquid absorbs the liquid. Since the cohesive force of the wetted powder is not so large as that of a solid layer, the portion of the layer formed by the wetted powder can be locally disengaged from the remaining portion of the layer. Thereby, the visible image formed by the liquid wetting the powder can be easily removed from the intermediate transfer belt, and is transferred onto the recording medium without deformation of the visible image.
The material may be a mixture of a plurality of kinds of powders. Additionally, the plurality of kinds of powders may include a first powder and a second powder, the first powder increasing the viscosity of the liquid, the second powder increasing an adhesive force of the image formed by the liquid.
Accordingly, the first powder serves to prevent the liquid from running on or penetrating into the recording medium, and the second powder serves to improve the adhesion of the visible image to the recording medium.
Additionally, according to another aspect of the present invention, a recording apparatus performing the above-mentioned method is provided.
According to one embodiment of the present invention, a recording apparatus records an image on a sheet-like recording medium having a first side and a second side opposite to the first side, the recording apparatus comprising:
an intermediate transfer belt carrying an image to be transferred onto the recording medium;
a liquid ejecting head ejecting droplets of a liquid toward the intermediate transfer belt;
an applicator applying a powder to a surface of the intermediate transfer belt so as to form a layer of the powder on the surface of the intermediate transfer belt, the powder being applied on the surface of the intermediate transfer belt prior to the application of the droplets of the liquid by the liquid ejecting head so that a visible image is formed by the droplets of the liquid on the layer of the powder, the powder absorbing the liquid so as to increase a viscosity of the droplets applied to the layer of the powder;
a transfer roller pressing the visible image on the intermediate transfer belt against the recording medium so as to transfer the visible image onto the recording medium;
a feeding mechanism feeding the recording medium so that the recording medium passes through a transferring position between the transfer roller and the intermediate transfer belt, the feeding mechanism including a first detector and a second detector, the first detector detecting an absence of an image on the first side of the recording medium and the second detector detecting an absence of an image on the second side of the recording medium, the feeding mechanism also including a switching mechanism to change a direction of feed of the recording medium so that the recording medium which has been passed through the transferring position can be returned to a position on the upstream side of the transfer roller and can be passed through the transferring position again, the recording medium being turned over while the recording medium is being returned to the position on the upstream side of the transfer roller; and
a control unit controlling operations of the intermediate transfer belt, the recording head and the switching mechanism so that the visible image is transferred onto at least one of the first and second sides of the recording medium based on outputs of the first and second detectors.
Other objects, features and advantages of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.